Use vb engine (api/functions) outside vbulletin directory

[waza]

hey, this is my situation:
my vb is located in root/forums/
I want to use vb engine (functions, classes) outside that folder for my index page.
So just root/index.php

In index I did
require_once("./forums/global.php");

But it doesn't work...

Is there a way to do this?

Btw, I know vbexternal, but that's not what I'm looking for.
grz,
seba